1. Field of the Invention
The present invention relates to a sheet conveying apparatus that corrects the skew and the width-direction position of a sheet and to an image forming apparatus that includes the sheet conveying apparatus.
2. Description of Related Art
Conventionally, to align a sheet with the position of an image to be formed on the sheet, an image forming apparatus includes a skew correction mechanism and a width-direction correction mechanism. The skew correction mechanism corrects the skew of the conveyed sheet, and the width-direction correction mechanism corrects the position of the sheet in a direction (sheet width direction) perpendicular to a sheet conveyance direction.
If a conveyed sheet is conveyed obliquely, the skew correction mechanism corrects and straightens the orientation of the sheet. If a sheet is displaced while being conveyed or during skew correction by the skew correction mechanism, the width-direction correction mechanism corrects the displacement from a conveyance reference position in the sheet width direction.
Japanese Patent Publication No. 58-101289 discusses a skew correction mechanism. According to this publication, to correct the skew of the leading edge of a conveyed sheet, an upper roller pair arranged upstream of a registration roller pair causes the leading edge of the conveyed sheet to come into contact with the registration roller pair and causes the sheet to form a loop. In addition, Japanese Patent Publication No. 58-101289 discusses a width-direction correction mechanism. According to this publication, to correct the sheet position in the sheet width direction, the registration roller pair shifts a straightened sheet in the sheet width direction while the sheet is pinched by an upstream roller pair and the registration roller pair.
However, if the sheet position in the sheet width direction is corrected by shifting the registration roller pair in the sheet width direction while being pinched, the sheet may be greatly twisted. As a result, the sheet may be wrinkled or torn.
To solve such a problem, Japanese Patent Application Laid-Open No. 2011-153032 discusses a sheet conveying apparatus that separates the upstream roller pair from the sheet when shifting the registration roller pair in the width direction to correct the sheet position in the sheet width direction.
However, the sheet conveying apparatus discussed in Japanese Patent Application Laid-Open No. 2011-153032 requires a mechanism for separating the upstream roller pair. Consequently, the apparatus is made complex and the cost is increased.